The present invention relates generally to fillers for asphalt composites such as roofing shingles, and more particularly relates to fly ash filler and filler blends for use in asphalt compositions and to methods for selecting or modifying a fly ash filler or filler blend for use in asphalt composites.
Asphalt shingle manufacturing plants typically utilize a mineral filler, or extender, both to impart desired mechanical properties to the shingles and to reduce raw material costs. The mineral filler typically used for this purpose is a fine particulate inorganic material, commonly produced from ground limestone or calcium carbonate, and is typically used at filler loadings of 60-65% by weight of the asphalt composite. The principal role of the filler in this application is to extend the more costly asphalt to improve the economics of the process, while at the same time stabilizing and stiffening the asphalt matrix to improve its resistance to extreme heat and weathering.
As an alternative to calcium carbonate, U.S. Pat. No. 5,565,239 to Pike entitled xe2x80x9cMethod of Making Asphaltic Roofing Material Containing Class F Fly Ash Fillerxe2x80x9d describes the use of Class F fly ash as a filler for asphalt roofing materials. The patent discusses a number of disadvantages associated with using calcium carbonate and a number of advantages associated with using fly ash as a filler in asphalt shingles. Although some Class F fly ashes could be used as fillers for asphalt shingles, many fly ashes that meet Class F specifications cannot be used with asphalt at loadings of 60-65% by weight to produce a composite that meets industry standards. Therefore, there is a need in the art to better determine what fly ashes can indeed be used as fillers with asphalt shingles. Furthermore, there is a need in the art to increase the filler loadings for asphalt shingles to increase the mechanical properties of the shingles such as the pliability, tensile strength and tear strength and to decrease cost.
The present invention provides a method for determining what fly ashes can be used as fillers for asphalt composites such as roofing shingles. In addition, the invention provides a fly ash filler or filler blend that can used in amounts of greater than 45% by volume and 70% by weight to increase mechanical properties of the asphalt composites such as pliability, tensile strength and tear strength while reducing the cost to produce the asphalt composites.
In accordance with the invention, the inventors have discovered that the granulometry of the fly ash used as a filler or in filler blends for asphalt composites such as roofing shingles is important to the rheological performance of the filled asphalt in the production of the asphalt composites and to the mechanical properties of the resulting asphalt composites. In one embodiment, the asphalt composite includes asphalt and a filler, the filler comprising a blend of fly ash and at least one other filler wherein the filler blend has a particle size distribution having at least three modes and typically having three modes. Preferably, the particle size distribution includes a first mode having a median particle diameter from 0.3 to 1.0 microns, a second mode having a median particle diameter from 10 to 25 microns, and a third mode having a median particle diameter from 40 to 80 microns. The particle size distribution also preferably includes 11-17% of the particles by volume in the first mode, 56-74% of the particles by volume in the second mode, and 12-31% of the particles by volume in the third mode. Moreover, the ratio of the volume of particles in the second and third modes to the volume of particles in the first mode is preferably from about 4.5 to about 7.5. The fly ash can, for example, be a lignite coal fly ash or a subbituminous coal fly ash. The fly ash can also have a carbon content of from 1% to 5% by weight. In one preferred embodiment, the at least one additional filler in the filler blend is a second fly ash. For this embodiment, the filler blend preferably comprises a high fine particle content fly ash filler (e.g. having a median particle size of 10 microns or less) and a low fine particle content fly ash filler (e.g. having a median particle size of 20 microns or greater). Alternatively, the at least one additional filler in the filler blend can be a calcium carbonate filler. In this particular embodiment, the fly ash is preferably a high fine content fly ash. The filler blend can include from about 10% to about 90% by weight of the fly ash filler and from about 90% to about 10% by weight of the calcium carbonate filler. The filler blend preferably has a packing factor of at least 65% and can be loaded in the asphalt composite at a filler loading of greater than 45% by volume or at a filler loading of greater than 70% by weight. The present invention further includes a filler for asphalt composites comprising fly ash and at least one additional filler and having the properties discussed above.
The present invention also includes a method for producing an asphalt composite, comprising combining asphalt with a fly ash and at least one additional filler such that the fly ash and the at least one additional filler together produce a filler blend having a particle size distribution with at least three modes and producing an asphalt composite with the resulting filled asphalt. Preferably, the method includes the step of blending the fly ash and the at least one additional filler together to produce a filler blend prior to the combining step. Alternatively, a fly ash blend formed by burning two or more types of coal selected from the group consisting of lignite coal, subbituminous coal and bituminous coal can be used to form the asphalt composite. The filler blends can include the fillers and the filler properties described in the previous paragraph. Preferably, the fly ash and the at least one additional filler can be combined with the asphalt to produce a viscosity of 6000 centipoise (cps) or less at 400xc2x0 F. when the fly ash filler is present in an amount of at least 45% by volume, at least 65% by weight, or even at least 70% by weight. The asphalt, fly ash and the at least one additional filler can also be combined with carbon to produce the asphalt composite. The fly ash used in the filler blend can be air classified to produce the fly ash filler for use in the filler blend. For example, a high fine particle content fly ash or a high coarse particle content fly ash can be air classified for use in the filler blend.
In another embodiment of the invention, the present invention comprises an asphalt composite comprising asphalt and a subbituminous coal fly ash filler, wherein the subbituminous coal fly ash filler has a particle size distribution having at least three modes and typically includes three modes. Preferably, the particle size distribution includes a first mode having a median particle diameter from 0.3 to 1.0 microns, a second mode having a median particle diameter from 10 to 25 microns, and a third mode having a median particle diameter from 40 to 80 microns. The particle size distribution also preferably includes 11-17% of the particles by volume in the first mode, 56-74% of the particles by volume in the second mode, and 12-31% of the particles by volume in the third mode. Moreover, the ratio of the volume of particles in the second and third modes to the volume of particles in the first mode is preferably from about 4.5 to about 7.5. The fly ash filler preferably has a packing factor of at least 65% and can be loaded in the asphalt composite at a filler loading of greater than 45% by volume or at a filler loading of greater than 70% by weight. Moreover, the subbituminous coal fly ash is typically a Class C fly ash. The present invention further includes a subbituminous coal fly ash filler for asphalt composites having the properties discussed above.
The present invention also includes a method for producing an asphalt composite, comprising the steps of combining asphalt with a subbituminous coal fly ash filler having a particle size distribution with at least three modes and producing an asphalt composite with the resulting filled asphalt. The subbituminous coal fly ash filler can have the properties discussed above. Preferably, the subbituminous coal fly ash filler can be combined with the asphalt to produce a viscosity of 6000 centipoise or less at 400xc2x0 F. when the fly ash filler is present in an amount of at least 45% by volume, at least 65% by weight, or even at least 70% by weight. The subbituminous coal fly ash can also be air classified to produce a fly ash filler having a particle size distribution having at least three modes. The subbituminous coal fly ash filler and asphalt can also be combined with carbon to produce the asphalt composite.
Moreover, the present invention includes an asphalt composite comprising asphalt and a filler at a loading of greater than 70% by weight, the filler comprising fly ash and having a particle size distribution with at least three modes and typically having three modes. The filler in the asphalt composite preferably has a particle size distribution such as described above. The fly ash can be a lignite coal fly ash or a subbituminous coal fly ash, and the asphalt composite can further include an additional filler such as a second fly ash or calcium carbonate. The present invention also includes a method for producing an asphalt composite, comprising the steps of combining asphalt and a filler at a loading of greater than 70% by weight, the filler comprising fly ash and having a particle size distribution with at least three modes, and producing an asphalt composite with the resulting filled asphalt.
The present invention further includes an asphalt composite comprising asphalt, a filler and a primarily carbon-containing material. The filler preferably has a particle size distribution with at least three modes and typically has three modes. More preferably, the filler has a particle size distribution such as described above. The filler can include a fly ash such as a lignite coal fly ash or a subbituminous coal fly ash, and can further include an additional filler such as a second fly ash or calcium carbonate. Alternatively, the filler can be calcium carbonate. The primarily carbon-containing material is preferably present in the asphalt composite in an amount from about 0.1% to about 5% by weight. In addition, the present invention includes a filler blend for asphalt composites including a filler and a primarily carbon-containing material. Moreover, the present invention includes a method for producing an asphalt composite comprising the steps of combining asphalt with a filler and a primarily carbon-containing material and producing an asphalt composite with the resulting filled asphalt.
The present invention also includes an asphalt composite comprising asphalt and a calcium carbonate filler, wherein the calcium carbonate has a particle size distribution having at least three modes and typically having three modes. Moreover, the present invention includes a method for producing an asphalt composite, comprising the steps of combining asphalt with a calcium carbonate filler having a particle size distribution having at least three modes and producing an asphalt composite with the resulting filled asphalt.
In another embodiment of the invention, the present invention includes a method for producing an asphalt composite, comprising the steps of classifying a fly ash to produce a fly ash having a particle size distribution having at least three modes, combining the fly ash with asphalt to produce a filled asphalt and producing an asphalt composite with the filled asphalt. The fly ash can be classified to produce a fly ash having a particle size distribution with three modes, wherein the modes preferably include a first mode having a median particle diameter from 0.3 to 1.0 microns, a second mode having a median particle diameter from 10 to 25 microns, and a third mode having a median particle diameter from 40 to 80 microns. More preferably, the classified fly ash has a particle size distribution that includes 11-17% of the particles by volume in the first mode, 56-74% of the particles by volume in the second mode, and 12-31% of the particles by volume in the third mode. The classified fly ash also preferably has a particle size distribution wherein the ratio of the volume of particles in the second and third modes to the volume of particles in the first mode is from about 4.5 to about 7.5. Moreover, the classified fly ash preferably has a packing factor of at least 65%. The classified fly ash can be a lignite coal fly ash, a subbituminous coal fly ash, a bituminous coal fly ash or a fly ash resulting from burning two or more of these coals. The classified fly ash and at least one additional filler can be combined with asphalt to produce a filled asphalt, e.g., by blending the fly ash and the at least one additional filler together to produce a filler blend. The filler blend can include a first fly ash and a second fly ash such as a blend of a high fine particle content fly ash and a low fine particle content fly ash. Alternatively, the filler blend can include a fly ash (e.g. a high fine particle content fly ash) and a calcium carbonate. Preferably, the filler blend includes from about 10% to about 90% by weight of fly ash and from about 90% to about 10% by weight of calcium carbonate. The classified fly ash can have a carbon content of from 1% to 5% by weight or, alternatively, carbon can be combined with the classified fly ash and asphalt. The classified fly ash (and optional additional filler) preferably combine with the asphalt to produce a filled asphalt having a viscosity of 6000 centipoise or less at 400xc2x0 F. at loadings of at least 45% filler by volume, at least 65% filler by weight, and even at least 70% filler by weight. The fly ash is preferably classified using an air classification method.
Furthermore, the present invention includes a method for producing an asphalt composite, comprising the step of selecting a fly ash filler for use in the asphalt composite or modifying a fly ash filler for use in the asphalt composite to have a particle size distribution with at least three modes to increase the packing factor of the fly ash filler and to improve the mechanical properties of the asphalt composite. Typically, the method comprises selecting a fly ash filler or modifying a fly ash filler to have a particle size distribution with three modes. The method can also include selecting an asphalt that has good compatibility with the fly ash filler to improve the mechanical properties of the asphalt composite. Moreover, a fly ash filler can be selected or modified to have a loss on ignition (or carbon content) within a certain desirable range to provide a desirable viscosity for the filled asphalt in processing and good pliability, tear strength and tensile strength for the asphalt composite. A fly ash filler can also be selected or modified to have a high specific gravity to increase the pliability of the asphalt composite. Further, fly ash filler can also be selected or modified to have a low oil absorption to decrease the viscosity of the filled asphalt in processing.
These and other features and advantages of the present invention will become more readily apparent to those skilled in the art upon consideration of the following detailed description, which describe both the preferred and alternative embodiments of the present invention.
In the following detailed description, preferred embodiments are described in detail to enable practice of the invention. Although the invention is described with reference to these specific preferred embodiments, it will be understood that the invention is not limited to these preferred embodiments. But to the contrary, the invention includes numerous alternatives, modifications and equivalents as will become apparent from consideration of the following detailed description.
As discussed above, the inventors have determined that the granulometry of fly ash fillers and filler blends is the dominant factor in determining the suitability of these fillers for use as mineral fillers in asphalt composites such as roofing shingles and allows these fillers to replace the ground limestone or calcium carbonate fillers conventionally used in asphalt composites. This discovery is in marked contrast to the generic xe2x80x9cchemicalxe2x80x9d description used in the U.S. Pat. No. 5,565,239, which classifies fly ash solely on the basis of its ASTM designation. In particular, U.S. Pat. No. 5,565,239 discusses the use of Class F fly ash fillers for asphalt shingles at a loading of 40 to 70% by weight. Although asphalt shingles filled at 40% with Class F fly ashes generally have acceptable mechanical properties, most Class F fly ash composites do not meet quality control specifications at greater than 60% by weight fly ash. Thus, U.S. Pat. No. 5,565,239 does not sufficiently describe the properties for fly ash that produce asphalt shingles having desirable performance.
As is well understood to those skilled in the art, fly ash is produced from the combustion of pulverized coal in electrical power generation plants. Fly ash is formed of mineral matter that is typically of very fine particle size, ranging from less than 1 micron to over 100 microns in some cases. The fly ash particles possess a substantially spherical shape as a consequence of the high temperature melting and coalescence in the furnace of the mineral matter accompanying the coal. The fine particle size and spherical shape are advantageous properties of the fly ash and are in marked contrast to the properties of ground limestone or calcium carbonate, which is typically relatively coarse with an irregular, blocky particle shape. These differences in granulometry between fly ash and limestone or calcium carbonate fillers are highly significant to the present invention.
Mineralogically, fly ash is predominantly amorphous, or non-crystalline, in nature as a result of the rapid quenching of clay/shale minerals as they rapidly pass through the boiler flame and dust collection system of the power plant. For some fly ashes, the amorphous material can be described as an aluminosilicate glass similar in composition to the mineral mullite (Al6Si2O13); for other fly ashes, it can be described as a calcium aluminosilicate glass similar in composition to the mineral anorthite (CaAl2Si2O8). Fly ashes also contain smaller amounts of a variety of other mineral components derived from thermal modification of accessory minerals present in the coal. These typically include mullite, quartz (SiO2), ferrite spinel (Fe3O4), hematite (Fe2O3), dicalcium silicate (Ca2SiO4), tricalcium aluminate (Ca3SiO5), and lime (CaO). These mineral components occur either as inclusions in the glass particles or as discrete particles.
It is commonly known that the chemical composition of fly ash changes as a result of the type of coal being burned in the boiler. These differences are largely in the relative proportions of the element calcium present in the ash. For example, high rank bituminous coals generally have a low calcium content and produce an ash with relatively low calcium, typically less than 5% as CaO; whereas low rank thermal coals generally have much higher content of calcium, typically in the range 8-20% CaO for lignite coals and 20-30% CaO, or higher, for subbituminous coals. These differences are recognized by ASTM specifications, such as ASTM C-618 that governs the use of fly ash as a pozzolan in concrete in the United States and elsewhere, and by Canadian specifications that classify the ashes based on their CaO content.
Current ASTM C-618 specifications include only two designations or classes of fly ash: xe2x80x9cClass Fxe2x80x9d and xe2x80x9cClass Cxe2x80x9d fly ashes. The xe2x80x9cClass Fxe2x80x9d designation generally incorporates fly ashes originating from the combustion of bituminous and lignite coals and the xe2x80x9cClass Cxe2x80x9d designation generally incorporates ashes from the combustion of subbituminous coals. These designations are based on the chemical composition of the fly ash in such a way that when the sum of the element oxides (SiO2+Al2O3+Fe2O3) derived from chemical analysis of the ash is equal to or greater than 70% by weight, then the fly ash is designated a xe2x80x9cClass Fxe2x80x9d fly ash. When the sum of the element oxides is equal to or greater than 50% by weight, the fly ash is designated as a xe2x80x9cClass Cxe2x80x9d fly ash.
In Canada, as mentioned above, fly ashes have certain designations based on their CaO content. In particular, a fly ash is considered a xe2x80x9cClass Fxe2x80x9d when it includes less than 8% CaO, a xe2x80x9cClass CIxe2x80x9d when it includes 8-20% CaO, and a xe2x80x9cClass CHxe2x80x9d when it includes greater than 20% CaO.
It is less commonly known that the particle-specific properties, or granulometry, of a fly ash also vary according to the source of the coal and the included mineral matter. In particular, this factor has a marked effect on the proportions of the fine and coarse particles present in the fly ash, also known as the particle size distribution, in concert with the surface area and particle packing characteristics. Significantly, these properties are not addressed by appropriate ASTM specifications, such as ASTM C-618, that cover the use of fly ash by industry.
Thus, fly ash is a chemically, physically and mineralogically complex material with properties that vary according to the source of the coal being burned in the power plant, as well as the combustion conditions and pollution control equipment installed at the power plant. An intimate knowledge of all these variables is essential to the successful use of fly ash as a mineral filler in asphaltic products such as asphalt shingles. Furthermore, it is necessary that the filled asphalt-fly ash composite meets applicable quality control specifications and ASTM performance criteria.
The present invention discloses a methodology for selecting or modifying a fly ash that will allow it to be used effectively as a substitute for the presently used crushed limestone or calcium carbonate fillers in asphalt composites. The inherent properties of fly ash, or modified fly ash, allow a more economical asphalt composite to be manufactured as well as one with superior performance.
In accordance with the invention, the inventors have discovered that the granulometry of the fly ash is important in determining whether the fly ash or a blend of the fly ash and another filler can be used to produce asphalt composites and to improve the properties of asphalt composites. In particular, a fly ash filler is selected for use in the asphalt composite having a particle size distribution with at least three modes to increase the packing factor of the fly ash filler and the mechanical properties of the asphalt composite. Alternatively, the fly ash can be blended with another fly ash or with another filler to modify the properties of the fly ash to produce a fly ash having a particle size distribution with at least three modes. Typically, the fly ash filler or filler blend has a particle size distribution with three modes but can have four, five or even more modes. In accordance with the invention, an asphalt having good compatibility with the fly ash filler or filler blends can be used to improve the mechanical properties of the asphalt composite. Moreover, a fly ash filler or filler blend having a loss on ignition (or carbon content) within a certain desirable range can be selected to provide a desirable viscosity for the filled asphalt in processing and good pliability, tear strength and tensile strength for the asphalt composite. A fly ash filler or filler blend can also be used having a high specific gravity to increase the pliability of the asphalt composite. Further, a fly ash filler or filler blend can also be used having a low oil absorption to decrease the viscosity of the filled asphalt in processing.
As mentioned above, it has been determined by the inventors that a filler having a particle size distribution with at least three modes has been found to be particularly advantageous for use with asphalt composites such as roofing shingles. Preferably, the particle size distribution has three to five modes and typically has three modes. Preferably, the particle size distribution includes a first mode having a median particle diameter from 0.3 to 1.0 microns, a second mode having a median particle diameter from 10 to 25 microns, and a third mode having a median particle diameter from 40 to 80 microns. In some cases, the filler can also include a coarse mode with a median particle diameter in the region of 100-200 microns and, in other cases, the filler can include an additional ultrafine mode with a median particle diameter in the region of 0.05-0.2 microns. The particle size distribution also preferably includes 11-17% of the particles by volume in the first mode, 56-74% of the particles by volume in the second mode, and 12-31% of the particles by volume in the third mode. Moreover, the ratio of the volume of particles in the second and third modes to the volume of particles in the first mode is preferably from about 4.5 to about 7.5. The filler also preferably has a packing factor of at least 65%, and typically has packing factors in the range of 65% to 75% and more typically in the range of 67% to 73%. The filler of the invention can advantageously be used at filler loadings of 65-70% by weight, and even greater than 70% by weight (e.g. even as high as 75% by weight). In addition, the filler of the invention can be used at filler loadings of greater than 45% by volume, greater than 50% by volume, and even as high as 55% by volume. As a result, the fillers of the invention can be used to replace significant amounts of asphalt in the asphalt composite and thus can greatly reduce the cost of the asphalt composite.
The filler used in accordance with the invention can include fly ash, calcium carbonate or a blend thereof. In addition, the filler can be a blend of two or more different fly ashes or two or more different calcium carbonates. Preferably, the filler used in accordance with the invention will be a lignite fly ash, a subbituminous ash (typically a class C ash), a bituminous ash, a blend of two or more fly ashes (e.g. a subbituminous/bituminous blend) or a blend of a fly ash and a calcium carbonate. More preferably, the filler is a lignite fly ash or a blend of a fly ash and an additional filler. These fillers have the particle size distribution and preferably the other properties discussed herein that have been found to be particularly advantageous for use with asphalt to form asphalt composites such as roofing shingles. The fly ash filler typically has a carbon content of from about 0.1% to about 15% by weight and can advantageously be selected to have a carbon content of from about 1% to about 5% by weight. It has been discovered that a carbon content greater than 5% can undesirably result in high viscosities when mixed with the asphalt and can result in a less pliable asphalt shingle. Although a filler having a carbon content less than 1% can advantageously be used with the invention, a carbon content of 1% or greater can result in an asphalt shingle having a greater tear strength and tensile strength and can be desirable. Alternatively, a lower carbon content fly ash can be used and a primarily carbon-containing filler material added as discussed in more detail below to provide a carbon content of about 1% to about 5%.
In one embodiment of the invention, the filler is a blend of a fly ash and at least one additional filler wherein the filler blend has a particle size distribution having at least three modes. The fly ash used in the filler blend can be a lignite coal fly ash, a subbituminous coal fly ash, a bituminous coal fly ash, or a blend thereof. The at least one additional filler in the filler blend is typically selected to enhance the particle size distribution or other properties of the fly ash.
In one embodiment of the invention, the additional filler in the filled blend is a fly ash. For example, the filler blend can include a high fine particle content fly ash filler such as a subbituminous coal fly ash (e.g. having a median particle size of 10 microns or less) and a low fine particle content fly ash filler such as a bituminous coal fly ash (e.g. having a median particle size of 20 microns or greater). In addition, other blends of fly ashes are possible such as bituminous/lignite, lignite/subbituminous and bituminous/lignite/subbituminous blends. In addition, two or more fly ashes from the same type of coal source, e.g., two different lignite coal fly ashes, can be blended to produce the filled blend of the invention. In the filler blends, the first fly ash can be included in an amount from about 0.1% to about 99.9%, more preferably from about 10% to about 90% by weight of the filler blend and the second fly ash can be included in an amount from about 99.9% to about 0.1%, more preferably from about 90% to about 10% by weight of the filler blend. The filler blend typically has a carbon content of from about 0.1% to about 15% by weight and can advantageously be selected to have a carbon content of from about 1% to about 5% by weight as discussed above. Although the fly ash filler blend can be produced by blending two different fly ashes, the fly ash filler blend can also be formed by burning at least two different coals selected from the group consisting of bituminous coals, lignite coals and subbituminous coals, and using the resulting ash as the filler blend. For example, a subbituminous coal and a bituminous coal can be burned together to produce the filler blend.
In another embodiment of the invention, the filler blend is a blend of a fly ash and another mineral filler such as calcium carbonate, slate dust, silica fume, and the like. In this embodiment, the filler is preferably calcium carbonate. The calcium carbonate is preferably combined with a high fine particle content fly ash filler such as a lignite or subbituminous fly ash (e.g. having a median particle size of 10 microns or less). The filler blend can include from about 0.1% to about 99.9%, more preferably about 10% to about 90% by weight of the fly ash and from about 99.9% to about 0.1%, more preferably about 90% to about 10% by weight of the calcium carbonate. The fly ash can also be selected to produce a filler blend having a carbon content of from 1% to 5% by weight as discussed above or a primarily carbon-containing material can be added to the filler blend as discussed in more detail below.
The fillers used in the invention can be classified to produce a filler having a particle size distribution with at least three modes as discussed above or one or more of the fillers used in the filler blend can be classified to allow the filler blend containing the filler to have a particle size distribution with at least three modes. For example, the fly ash fillers used alone or in the filler blends can be classified to produce the desired particle size distribution. For example, a high fine particle content fly ash such as a subbituminous coal ash or a high coarse particle content fly ash such as a bituminous coal ash can be air classified to provide the desired particle size distribution. In addition to air classification, the fly ash fillers can be classified using dry screening (sieving) or wet classification methods (e.g. wet screening or hydrocyclones) followed by drying of the fly ash. Alternatively, in-plant classification methods can be used. For example, the fly ash fillers can be classified electrostatically by adjusting the collection methods of the electrostatic precipitators used to recover the fly ash from the electric power generation plants. In addition, the fly ash fillers can be classified by modifying the discharge hopper selection of the fly ash from the electric power generation plants.
The filler and the asphalt can optionally be combined with a primarily carbon-containing material (including, e.g., 50% or more carbon by weight) to impart greater tear strength and tensile strength to the asphalt composite. The primarily carbon-containing material can be an amorphous carbon such as a carbon black, a partially graphitized carbon, or a by-product carbon or carbon concentrate from an industrial process. The primarily carbon-containing material can be added to the filler and the asphalt in an amount of about 0.1% to about 5% by weight, and in addition to the filler preferably produces a total carbon content of about 1% to about 5% by weight.
The present invention also includes a method for producing an asphalt composite that includes the steps of combining asphalt with the filler to produce a filled asphalt and producing an asphalt composite with the resulting filled asphalt. Because the asphalt is processed at an elevated temperature (e.g. 350-450xc2x0 F. and typically 400-425xc2x0 F.) for use in the asphalt composites, the filler is typically preheated prior to adding it to the asphalt. Advantageously, by virtue of their lower specific heats, the fly ash fillers and fly ash filler blends used in the invention can be preheated using less energy than calcium carbonate fillers and thus can be processed at a lower cost. When the filler is a filler blend, each of the fillers can be added separately to the asphalt but preferably the filler blend is prepared prior to being added to the asphalt so the fillers can be preheated together. For example, the fly ash filler and at least one additional filler can be blended together to form the filler blend prior to preheating the filler blend and combining the filler blend with the asphalt. Alternatively, a fly ash blend can be formed by burning two or more types of coal selected from the group consisting of lignite coal, subbituminous coal and bituminous coal (e.g. by burning a subbituminous coal and a bituminous coal together) and used as the filler blend for the asphalt composite.
The filled asphalt preferably has a sufficiently low viscosity to allow it to be processed to form the asphalt composite. Molten asphalt can be processed at various temperatures known in the art and is preferably processed at a temperature between 350 and 450xc2x0 F. and typically between 400 and 425xc2x0 F. (e.g. 400xc2x0 F.). Typically, asphalt has a viscosity of about 400 centipoise at these processing temperatures. When the filler is added to asphalt, the viscosity increases. Preferably, the filled asphalt has a viscosity below a particular threshold (e.g. between 5000 and 7000 centipoise) at the desired loadings so it can be effectively processed into the asphalt composite. Preferably, the fly ash fillers and filler blends used in the invention produce a viscosity of 6000 centipoise or less at 400xc2x0 F. when the fly ash filler is added at the desired loadings. For example, the filler of the invention can advantageously be used at filler loadings of 65-70% by weight, and even greater than 70% by weight (e.g. even as high as 75% by weight) to produce the desired viscosity. The filler of the invention can also be used as filler loadings of greater than 45% by volume, greater than 50% by volume, and even as high as 55% by volume, to produce the desired viscosity. As a result, the fillers of the invention can be used to replace significant amounts of asphalt in the asphalt composite and thus can greatly reduce the cost of the asphalt composite. Alternatively, the asphalt can be heated to lower temperatures to produce the desired viscosity at the same filler loadings conventionally used in asphalt composites. Thus, the thermal history of the asphalt composite can be minimized.
The filled asphalt can be prepared and the asphalt composite can be prepared from the filled asphalt by methods known in the art such as the methods described in U.S. Pat. No. 5,565,239. For example, the filled asphalt can impregnate a glass fiber mat on a moving conveyor system to produce an asphalt composite. Coating granules can then be added to the asphalt composite and the resulting asphalt composite can be allowed to cool and harden to form the roofing shingles.
The present invention will now be further demonstrated by the following non-limiting examples.